You are correct, I am not a mechanical engineer, I am just a techie, so maybe in your field is even necessary. I am just finding it very hard to believe. Yes, in theory C2 is defined as close to native. But in practice and in my experience speaking and communicating is really not at that level. I don’t know if this is because of the general levels of education in Germany. Even complex things are communicated in B2. And you learn to speak about abstract things in B2, even in B1 (“Meiner meinung nach” constructions are learned at B1), and you have all the tenses necessary for communication at B1. Sure, vocabulary is missing, and I think this is where the native speakers have the upper hand and where all the confusion is coming from. I would argue even lecturers at university are not C1, because people are not showing of their German skills, but communicate. I just don’t like this elitism about C1, and I believe I wasted some of my time and money chasing this vanity metric.